The invention relates to an internal combustion engine with at least one reciprocating piston in which a combustion chamber is located which is divided into two or more partial chambers by restrictions extending to the bottom of the combustion chamber, the said partial chambers being shaped asymmetrically as seen from above and being arranged rotation-symmetrically to an axis passing through the center of the combustion chamber and being parallel to the longitudinal axis of the piston, with a minimum distance in the restricted area of the wall of the combustion chamber and a maximum distance in concave-shaped areas of the wall of the combustion chamber, as measured in a cutting plane directly below the piston head, departing from the axis of the combustion chamber, the ratio between minimum distance and maximum distance being greater or equal 0.2.
In extremely lean operation of gas engines emissions of nitrogen oxides may be kept as low as in stoichiometric operation with a three-way catalytic converter, while the internal efficiency is higher and the thermal loads of the components are lower.
Lean mixtures burn at a lower rate, however, which is a disadvantage from the point of view of thermodynamics and leads to fluctuations in the combustion pressure between cycles. An efficient means of increasing the combustion rate is an increase in the turbulent portion of the flow inside the cylinder.